Black Widow long fin (Gymnocorymbus ternetzi long fin) — 3-4,5cm

Overview

The Black Widow long fin (Gymnocorymbus ternetzi long fin) is a striking and distinctive tetra variety for sale UK, featuring dramatically extended flowing fins that enhance the classic Black Skirt Tetra's elegant appearance. This long-finned variety showcases the same iconic black vertical stripes and silvery-grey body as the standard form, but with gracefully elongated dorsal, anal, and caudal fins that create a veil-like effect as the fish moves through the aquarium. A popular and hardy South American tetra, this variety adapts well to community aquariums and displays fascinating schooling behavior. With proper care and appropriate tankmates that won't nip those magnificent long fins, this attractive variety brings dramatic movement and presence to planted freshwater setups.

Appearance

Gymnocorymbus ternetzi long fin presents the distinctive Black Widow pattern—a silvery-grey body adorned with three prominent vertical black bands that become more defined with age. The long fin variety displays dramatically extended finnage, with flowing dorsal, anal, and caudal fins that create an elegant veil-like appearance. Juveniles show more intense black coloration that fades somewhat as fish mature, though the vertical banding remains striking. The extended fins flow gracefully with movement, creating spectacular visual impact when schools move in unison. Eyes are proportionally large. Sexual dimorphism can be subtle; males typically have slightly broader anal fins and slimmer bodies than fuller-bodied females. The overall effect is one of dramatic elegance—classic Black Widow patterning enhanced by flowing finnage.

Natural Habitat

The base species Gymnocorymbus ternetzi inhabits slow-moving rivers, streams, and floodplain areas in the Paraguay and Guaporé River basins of South America, including regions of Brazil, Paraguay, Bolivia, and Argentina. In nature, these tetras form schools in areas with dense aquatic vegetation, submerged roots, and overhanging plants. The water ranges from soft to moderately hard, slightly acidic to neutral, with moderate temperatures. The long fin variety is a selectively bred aquarium strain developed for enhanced finnage. Natural populations feed on small invertebrates, insect larvae, worms, and plant matter. The complex vegetated habitat provides both foraging opportunities and shelter from predators.

Aquarium Setup

A minimum 80-litre aquarium provides adequate space for a school of 6-8 individuals, allowing room for their extended finnage. Create a planted community setup with fine sand or small gravel substrate, driftwood for structure, and moderate to generous planting including background and midground species. Maintain substantial open swimming space through the center where schools can display natural behavior without damaging delicate long fins. Lighting should be subdued to moderate—floating plants help diffuse bright light and make fish more comfortable. Filtration should provide gentle water movement without creating strong current that will stress long-finned varieties. Avoid sharp decorations or rough surfaces that could tear delicate finnage. A secure lid is essential, as these are capable jumpers. Include natural tannin sources like Indian almond leaves or driftwood to create slightly acidic water that enhances health.

Water Parameters

Maintain soft to neutral water conditions. Target pH of 6.0-7.5, with soft to moderately hard water (up to 15 dGH) acceptable—this adaptable species tolerates a range of conditions. Temperature should remain stable at 22-26°C using a reliable heater. Water quality must be excellent: ammonia and nitrite always zero, nitrates below 20 ppm through regular 25-30% weekly water changes. Use dechlorinated water matched to tank parameters. While hardy and adaptable, this species shows best health and finnage development in softer, slightly acidic conditions. Maintain stability—avoid sudden parameter shifts. Long-finned varieties may be slightly more sensitive to poor water quality than standard forms, as damaged fins are susceptible to bacterial infection. Regular water testing and consistent maintenance ensure optimal health and finnage condition.

Feeding

Offer a varied omnivorous diet including quality flake or small pellet foods as a staple, supplemented regularly with frozen and live foods such as daphnia, brine shrimp, bloodworms, and tubifex. Include some vegetable matter or spirulina-enriched foods for balanced nutrition. Feed two to three times daily in moderate portions that can be consumed within 3-5 minutes. This species is an enthusiastic, unfussy feeder that readily accepts most prepared foods. Variety maintains optimal health, coloration, and finnage condition. Long-finned varieties benefit from sinking foods as well as floating foods, as the extended finnage can make surface feeding slightly more challenging. Observe feeding to ensure all fish receive adequate nutrition. Well-fed fish display better color, more confident behavior, and healthier finnage growth. Include vitamin-enriched foods to support fin regeneration if damage occurs.

Behaviour

Black Widow long fin tetras display semi-active schooling behaviour. In proper schools, they form loose groups that move together through planted aquascapes, though schooling may be less tight than in some tetra species. The extended finnage creates graceful, flowing movement. Generally peaceful with appropriate tankmates, though can show minor fin-nipping behavior toward other long-finned fish if kept in too-small groups or cramped conditions. Active during daylight hours, occupying mid-water levels. In well-planted tanks with proper group sizes, behavior is confident and natural. Schooling behavior improves when fish feel secure—subdued lighting and planted refuge areas encourage natural activity. The long fins may make them slightly less active swimmers than standard-finned varieties. Compatible with diverse peaceful community species when housed appropriately.

Tank Mates

Ideal tank mates include peaceful tetras without fin-nipping tendencies, rasboras, peaceful Corydoras catfish, peaceful loaches, Otocinclus, and peaceful livebearers. Other peaceful South American species make natural companions. CRITICAL: Avoid housing with known fin-nippers including Tiger Barbs, Serpae Tetras, some cichlids, and other species with reputations for nipping—the extended fins are vulnerable to damage. Also avoid slow-moving fish with very long fins if these Black Widows show any nipping behavior, very small fry or shrimp, aggressive cichlids, large barbs, and fish large enough to eat them. The key is selecting peaceful, non-aggressive community species. In well-balanced communities with proper group sizes and no fin-nippers, this variety coexists peacefully and contributes dramatic finnage and movement to planted aquariums.

Breeding

Scatter-spawning egg layer that can be bred in dedicated breeding setups with appropriate conditions. To encourage breeding, set up a separate breeding tank (40-60 litres) with soft, slightly acidic water (pH 6.0-6.5), subdued lighting, fine-leaved plants like Java moss or spawning mops for egg deposition, and gentle sponge filtration. Condition adults with high-quality live and frozen foods until females become noticeably rounded with eggs. Introduce a conditioned pair in the evening. Spawning typically occurs at dawn, with eggs scattered among plants. Remove adults immediately after spawning, as they may eat eggs and fry. Eggs hatch in 18-36 hours depending on temperature. Fry become free-swimming 3-4 days after hatching and require microscopic foods like infusoria or liquid fry food initially, graduating to newly hatched brine shrimp within one week. Maintain excellent water quality during fry-rearing. Fry initially show standard finnage—long fins develop as they mature. Select for best finnage when growing out if breeding for show quality.

Why Buy from Tropical Fish Co

Tropical Fish Co specializes in quality South American tetras, including distinctive varieties like the Black Widow long fin. Every fish undergoes thorough quarantine and health screening with particular attention to finnage condition. Our expert team provides comprehensive guidance on long-finned species care, compatible tankmate selection, and community aquarium design to protect those magnificent flowing fins. We offer secure next-day delivery throughout the UK with professional insulated packaging and seasonal temperature control. Our commitment includes healthy fish with excellent finnage quality, backed by our live arrival guarantee and ongoing support. Whether establishing your first community aquarium or adding striking varieties to an existing collection, trust Tropical Fish Co for exceptional quality, expert advice, and customer service that stands behind every fish. Bring dramatic flowing elegance into your planted aquarium with confidence.